Get the banshee and fly until you get to Canyon B, where a covenant dropship comes down with two ghosts on it. Go up to the top of the center spire and take the other banshee. (If you are playing on co-op mode, push the other banshee off the cliff for your partner to use.) Destroy all remaining forces in the area, then fly through the tunnel to the area where you normally have to leave the tank. Save the marines and fly your banshee over the brown building that has the pillars at its base. Kill the covenant, then instead of going through the door, fly up to the bridges overhead. One bridge will have two green doors. Go through either door. Now there will be no enemies, and there will be all vehicles except mortar tanks at your disposal. This trick can help a little on Legendary mode.